The invention relates to a piston pumps and more particularly to an improved piston pump, which is particularly useful as a slip-controlled hydraulic vehicle brake system.
Piston pumps of the type with which this invention is concerned as shown, for example in DE 41 07 979 A1. This known piston pump has a pump housing with a pump bore in which a piston can be guided so that it can move axially, directly in this pump bore, or indirectly in a liner inserted into the pump bore. The pump bore and/or the liner constitute a piston guide. In order to deliver fluid, the piston can be driven to execute a reciprocating stroke motion. The known piston pump has a drive element in the form of a cam that can be driven to rotate, whose circumference the piston rests against with its end. A piston restoring spring inserted into the pump bore presses the piston against the circumference of the cam and holds the piston in contact with the circumference of the cam. In order to control a fluid flow direction through the piston pump, the piston pump has a valve, which is usually embodied as a spring-loaded check valve and constitutes an inlet or outlet valve of the piston pump.
The piston of the piston pump according to the invention has a valve seat part that has a valve seat of the valve controlling the fluid flow direction through the piston pump and a piston seal, which is of one part with the valve seat part and seals the piston, in particular on its high-pressure side, in the piston guide. This eliminates the need for a separate seal and saves the costs of manufacturing a groove to contain the seal and inserting the seal into the groove.
In addition, the piston of the piston pump according to the invention has a support body, for example a tubular or annular support body which is engaged by the restoring spring and by means of which the restoring spring presses the piston against the circumference of the cam driving the piston or against another drive element. The support body is supported against the valve seat part spaced apart from the valve seat and spaced apart from the piston seal of the valve seat part. The support body produces a uniformly distributed transmission of the force exerted on the valve seat part by the restoring spring and thereby prevents a deformation or damage to the valve seat part, particularly when this valve seat part is comprised of plastic. Since the support body introduces the force of the restoring spring into the valve seat part spaced apart from the valve seat and from the piston seal, the valve seat and the piston seal are protected completely or as much as possible from the force exerted by the restoring spring. A deformation of or damage to the valve seat and the piston seal by the force of the restoring spring is prevented; the use of the support body prevents the function and tightness of the valve seat and the piston seal from being impaired. The support body according to the invention permits the force of the restoring spring to be introduced into the valve seat part with a sufficient distance from the valve seat and the piston seal despite the usually small dimensions of the pistons of piston pumps for slip-controlled hydraulic vehicle brake systems. Pistons of this kind may have a diameter of 5 mm, for example.
The invention permits a small and compact design of the piston pump. Other advantages are the fact that it is manufactured from simple and inexpensively producible components and is comprised of a small number of components. The piston is optimized with regard to its manufacture while simultaneously retaining its full functionality.
The support body for the restoring spring may simultaneously constitute a retainer and/or a guide for a valve closing body of the valve, which is affixed to the piston and controls the fluid flow direction through the piston pump.
When this valve is embodied as a spring-loaded check valve, a valve closing spring of the valve is supported on the support body. This reduces the number of required components and achieves the fact that the valve closing spring does not have any negative influence on the valve seat.
In order to achieve, despite the small size, the greatest possible distance between the engagement point of the support body with the valve seat part from both the valve seat and the piston seal, the support body may engage the bottom of a groove between the valve seat part and the piston seal, which is embodied as a sealing lip.
The piston can be embodied of one piece with the valve seat part. The piston pump may have a piston that is comprised of a plurality of parts, essentially of two parts. The piston includes a sleeve-like shaped part that is closed at one end and open at the other, which is manufactured, for example, by deep drawing, cold forming, or extrusion. The use of a shaped part has the advantage that it can be simply, rapidly, and inexpensively produced in a single work step. In order to increase wear resistance, the shaped part can be hardened and an additional processing/finishing of the shaped part can be eliminated, in particular a costly cutting machining of the shaped part. The shaped part rests with its closed end against the circumference of the cam driving the piston or against another drive element.
The valve seat part is inserted, for example press-fitted, into the open end of the shaped part and can be manufactured inexpensively and simply, for example out of plastic. If the valve seat part is made of plastic, for example, the shaped part into which the valve seat part is inserted lends the valve seat part sufficient strength to withstand the stresses that occur during operation of the piston pump. The valve seat part has the valve seat for the valve that controls the fluid flow direction through the piston pump.
The piston pump according to the invention is particularly provided as a pump in a brake system of a vehicle and is used in the control of pressure in wheel brake cylinders. The abbreviations ABS, ASR, VDC, or EHB are used for such brake systems, depending on the type of brake system. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to supply brake fluid from a storage tank into a wheel brake cylinder or a plurality of wheel brake cylinders (ASR, VDC, or EHB). The pump is required, for example, in a brake system with wheel slip control (ABS or ASR) and/or a brake system serving as a steering aid (VDC) and/or an electrohydraulic brake system (EHB). With wheel slip control (ABS or ASR), for example, a locking of the wheels of the vehicle during a braking event when there is strong pressure on the brake pedal (ABS) and/or a spinning of the driven wheels of the vehicle when there is strong pressure on the gas pedal (ASR) can be prevented. In a brake system that serves as a steering aid (VDC), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal, for instance to prevent the vehicle from breaking out of the path desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB) in which the pump supplies the brake fluid into the wheel brake cylinder or cylinders if an electrical brake pedal sensor detects an actuation of the brake pedal or in which the pump is used to fill a reservoir of the brake system.